1. Field of the Invention
The invention concerns a spacing profile for a spacing frame which is to be fitted in the edge area of a double-glazing unit, forming an interspace, with a profile body of material possessing low thermal conductivity and with a diffusion-impermeable metal foil, which is joined to the profile body to establish a material fit.
2. Description of the Prior Art
Within the scope of the invention, the panes of the double-glazing unit are normally glass panes of inorganic or organic glass, without of course the invention being restricted thereto. The panes can be coated or finished in any other way in order to impart special functions to the double-glazing unit, such as increased thermal insulation or sound insulation.
The profile body of the spacing profile of material possessing low thermal conductivity constitutes, in respect of volume, the main part of the spacing profile and imparts its cross-sectional profile to it.
By "bonded to establish a material fit" is meant that the profile body and the metal layer are durably bonded to one another, for example by coextrusion of the profile body with the metal layer or by laminating the metal layer on separately, if necessary by means of a bonding agent or similar methods.
For some considerable time it has also been the practice to make use of plastic spacing profiles instead of metal spacing profiles for the manufacture of high thermal-insulation double-glazing units in order to take advantage of the low thermal conduction of the former materials.
By materials with low thermal conductivity in the sense of the invention should be understood those which evidence a coefficient of thermal conductivity which is significantly reduced in comparison with metals, that is to say by at least a factor of 10. The coefficients of thermal conductivity .lambda., for such materials are typically of the order of 5 W/(m*K) and below; preferably, they are less than 1 W/(m*K) and more preferably less than 0.3 W/(m*K). Plastics generally fall within this definition.
Of course, plastics generally possess low impermeability to diffusion in comparison with metals. In the case of plastic spacing profiles, it is necessary therefore to ensure by special means that atmospheric humidity present in the environment does not penetrate into the interspace to the extent that the absorption capacity of the desiccant generally accommodated in the spacing profiles is not soon exhausted, thus impairing the reliability performance of the double-glazing unit. Furthermore, a spacing profile must also prevent filler gases from the interspace, such as for example argon, krypton, xenon, sulphur hexafluoride, escaping from it. Vice versa, nitrogen, oxygen, etc., contained in the ambient air should not enter the interspace. Where impermeability to diffusion is involved below, this means impermeability to vapor diffusion, as well as impermeability to gas diffusion for the gases stated.
To improve impermeability to vapor diffusion, it is known from DE 33 02 659 A1, which has been employed for formulation of the preamble of claim 1, to provide a plastic spacing profile with a vapor barrier by applying to the plastic profile, on the side facing away from the interspace in installed state, a thin metal foil or a metallized plastic foil. This metal foil must span the interspace practically fully so that the desired vapor barrier effect will occur. Generally, the metal foil will be extended into the regions of the surfaces of the contact flanges of the spacing profile through which the profile is bound to the pane surfaces with the aid of a layer of sealing material.
EP 0 430 889 A2 suggests in the same context to provide a plastic spacing profile with a vapor diffusion impermeable layer by applying to the plastic profile, on the side facing away from the interspace in installed state, a thin layer, for example of chromium or a chrome-nickel alloy, by means of a physical coating process, for example by sputtering. These manufacturing processes are on the one hand complex and expensive, but on the other hand as well, are the only ones to permit production of extremely thin vapor-diffusion impermeable layers at acceptable cost.
Nowadays, preferably one part spacing frames are made from spacing profiles which are bent at three corners and at which the connection of the end parts is accomplished by corner joints or a straight joint, respectively, inserted into the end parts. One endeavors to accomplish the bending of the corners as simply as possible in terms of production technique, in particular without prior costly heating. The profiles of EP 0 430 889 A2 are not susceptible for spacing frames to be fabricated in this manner. The vapor-diffusion impermeable layers applied therein with thicknesses of 70 to 400 nm do not possess the necessary tearing resistance.
To enable cold bending of spacing profiles made of materials possessing low thermal conductivity, spacing profiles have been developed in which the profile body of material possessing low thermal conductivity is bonded to establish a material fit with a plastically deformable reinforcing layer, preferably a metal foil. This reinforcing layer may also be diffusion impermeable and span the entire width of the interspace, whereby the required diffusion impermeability of the spacing profile is achieved. A spacing profile of this type has been introduced under the name THERMOPLUS.RTM. TIS.RTM. for example in prospectus "Impulse fur die Zukunft (Impulses for the Future)" of Flachglas AG and is described in DE 298 14 768 U1. The reinforcing layer imparts good cold-bendability to the spacing profile to manufacture the above mentioned one-part spacing frames. It has, however, been found that the tinplate layer used for the reinforcing layer is not sufficiently corrosion resistant. It has been observed that the tinplate layer sometimes is already partly corroded when arriving at the insulating glass manufacturer, if it has been imparted to water or high air humidity before.